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Tune is attached. I have my VE table dialed in pretty well -- AFRs are nearly spot on and everything is pretty smooth. However, the VE table itself is relatively unusual:
To my understanding, the VE table should exclusively increase with increase in RPM and increase in MAP. This clearly doesn't seem to be the case with my motor. Above 6000 RPM Autotune pulls fuel and there is a "hotspot" between 50kPa and 140kPa where VE is higher. Here is my fuel system:
DW200 Pump
ID1050x Injectors
New Fuel Filter
AN6 Lines
Flex Fuel Sensor
Fuelab 515 Series AFPR (43.5PSI base pressure)
I've got all of my injector settings configured properly with the MegaSquirt settings straight from ID themselves. Include AFR Target is enabled. MAT Air Density table is zeroed out. Any ideas as to what could cause my VE table to look like this and should I even care as long as AFRs are correct?
The numbers in your ve table aren't the actual VE of the engine. They're just a value used in the equation that determines how long to energize the injector coils.
What makes you think a turbo will increase VE? In actuality a turbo reduces VE due to exhaust back pressure. If you have incorporate AFR turned on (which you should) then numbers under 100% are expected.
Your VE values raise as your engine becomes more efficient, then they plateau and drop as you increase RPM past the efficient point.
This is why a Dyno graph goes up (engine becomes more efficient as it flows better etc), peaks then goes down (as it can't flow enough anymore at higher RPM), and hence fueling follows the same trend, because more Torque/HP requires more fuel, so as you become less efficient (VE) you need less fuel.
In terms of VE, it should never go above 100%, unless you are doing sneaky stuff to workaround some limitation you have encountered. This is rare.
This is because an engine can never be more than 100% efficient, even with a turbo. VE is Volumetric Efficiency, it is the VOLUME of air that makes it into your cylinder(s) versus the maximum volume (displacement) of your engine.
A 1.6L engine sucking 1.6L of air is 100% volumetrically efficient. It is not possible to get more than 1.6L of air into a 1.6L container, even at higher pressure, it is still only 1.6L of air, because that's what Volume is.
The Speed Density equation your ECU uses, takes into account the volumetric efficiency of the engine (to determine volume of AIR that will enter the engine), it then uses the Air Temperature and the Manifold Absolute Pressure to determine the density of the air.
It can then use the Volume of air that entered the engine and how dense that air is to calculate the MASS of air in the engine, and make an assumption on how much Oxygen is in that air based.
From there (assuming you use Incorporate AFR) it can choose (based on your desired Air Fuel Ratio) what MASS of fuel to deliver in order to achieve the desired Air Fuel Ratio.
This is why it will never go over 100%, because even when boosted it is just the same volume at higher pressure, boost does affect your VE and requires retuning even at some non-boosted areas but cannot not increase your VE past 100%.
You engine still makes more power because there is more MASS of air, but there is not more VOLUME of air.
A thing to note, some reasons VE would show above 100 on your VE table are either some of your other modifiers are incorrect, i.e. something is pulling fuel resulting in you needing to trick the ECU into thinking it's getting more air than it actually is to calculate the required fuel.
This could be an enrichment value being incorrect, an air density value being incorrect, your O2 sensor reading incorrectly when tuning, your Required Fuel value being incorrect and not matching your injector size and engine displacement. There are many others.
Or you tuned without Incorporate AFR at an AFR other than 14.7 (because without it, the ECU is assuming 14.7 as AFR, based on REQ FUEL).
Or you're doing something special to either get more resolution by fudging numbers, but if your doing this you should know what your doing anyway and don't need to read this.
Hope this gives some insight into how it is actually working, as I find it helps tuning when you know why things are as they are.
Your VE values raise as your engine becomes more efficient, then they plateau and drop as you increase RPM past the efficient point.
This is why a Dyno graph goes up (engine becomes more efficient as it flows better etc), peaks then goes down (as it can't flow enough anymore at higher RPM), and hence fueling follows the same trend, because more Torque/HP requires more fuel, so as you become less efficient (VE) you need less fuel.
In terms of VE, it should never go above 100%, unless you are doing sneaky stuff to workaround some limitation you have encountered. This is rare.
This is because an engine can never be more than 100% efficient, even with a turbo. VE is Volumetric Efficiency, it is the VOLUME of air that makes it into your cylinder(s) versus the maximum volume (displacement) of your engine.
A 1.6L engine sucking 1.6L of air is 100% volumetrically efficient. It is not possible to get more than 1.6L of air into a 1.6L container, even at higher pressure, it is still only 1.6L of air, because that's what Volume is.
The Speed Density equation your ECU uses, takes into account the volumetric efficiency of the engine (to determine volume of AIR that will enter the engine), it then uses the Air Temperature and the Manifold Absolute Pressure to determine the density of the air.
It can then use the Volume of air that entered the engine and how dense that air is to calculate the MASS of air in the engine, and make an assumption on how much Oxygen is in that air based.
From there (assuming you use Incorporate AFR) it can choose (based on your desired Air Fuel Ratio) what MASS of fuel to deliver in order to achieve the desired Air Fuel Ratio.
This is why it will never go over 100%, because even when boosted it is just the same volume at higher pressure, boost does affect your VE and requires retuning even at some non-boosted areas but cannot not increase your VE past 100%.
You engine still makes more power because there is more MASS of air, but there is not more VOLUME of air.
A thing to note, some reasons VE would show above 100 on your VE table are either some of your other modifiers are incorrect, i.e. something is pulling fuel resulting in you needing to trick the ECU into thinking it's getting more air than it actually is to calculate the required fuel.
This could be an enrichment value being incorrect, an air density value being incorrect, your O2 sensor reading incorrectly when tuning, your Required Fuel value being incorrect and not matching your injector size and engine displacement. There are many others.
Or you tuned without Incorporate AFR at an AFR other than 14.7 (because without it, the ECU is assuming 14.7 as AFR, based on REQ FUEL).
Or you're doing something special to either get more resolution by fudging numbers, but if your doing this you should know what your doing anyway and don't need to read this.
Hope this gives some insight into how it is actually working, as I find it helps tuning when you know why things are as they are.
This is extremely helpful! That does make much more sense -- that is a cat-worthy response!
10-20-2021, 11:40 AM
Odd Autotune VE Table
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